On-the-Fly Calculation of Absorbed and Equivalent Atmospheric Radiation Dose in A Water Phantom with the Atmospheric Radiation Interaction Simulator (AtRIS)

Abstract

Computation of the ionization and radiation dose in arbitrary (exo-) planetary atmospheres due to energetic particles is recently becoming more important due to several reasons that are either correlated with the detection of trace gases for life on exoplanets or with computing dose rates at arbitrary altitudes in the Earth atmosphere. We previously presented Atmospheric Radiation Interaction Simulator, a new Geant4-based code tailored specifically to enable parametric studies of radiation propagation through exoplanetary atmospheres (Banjac et al., 2019 https://doi.org/10.1029/2018JA026042). Therein, the calculation of ion-electron pair production rates, which are a mandatory input for chemical and atmospheric modeling, has been presented and validated against Earth measurements and also other, similar, but solar-system-specific Geant4-based codes (PLANETOCOSMICS). In addition to providing input for atmospheric modeling of exoplanets, with AtRIS we aim to directly characterize the habitability by calculating the absorbed dose. In this technical validation study, after showing a detailed analysis of the secondary particles contributing to the atmospheric radiation, we describe a feature of the code which makes direct parametric studies of the interrelation of incident radiation and the resulting absorbed dose throughout the atmosphere possible. In a validation case study configured using an atmospheric model obtained with NRLMSISE-00 and a primary proton and helium GCR flux calculated using a recent improvement of the force-field approach, we have compared simulation results with measurements obtained with the Flight Radiation Environment Detector (FRED). We show that Atmospheric Radiation Interaction Simulator (AtRIS) can reproduce the measured dose rate dependence on altitude.